PID-based torque phase control of a power downshift

Abstract

A method for controlling the torque phase of a clutch-to-clutch power downshift in a vehicle includes determining, during a near-sync boost (NSB) state of the power downshift, a synchronization speed. The method includes estimating, via a controller, a feed-forward clutch pressure that holds a speed of the turbine at the synchronous speed, and then ramping a clutch pressure command to the oncoming clutch to the calculated feed-forward clutch pressure. Closed-loop proportional-integral-derivative (PID) control is initiated over the clutch pressure command during the NSB phase in response to a predetermined PID activation event. A vehicle includes an engine, transmission, torque converter, and a controller. The controller has a processor and memory on which instructions embodying the above method are recorded. Execution of the instructions by the processor causes the controller to execute the method.

The invention claimed is: 
     
       1. A method for controlling the torque phase of a clutch-to-clutch power downshift in a vehicle having a transmission and a torque converter, the method comprising:
 determining, during a near sync boost (NSB) state of the power downshift, a synchronization speed of an offgoing clutch and an oncoming clutch of the transmission, wherein the NSB state is a portion of the torque phase that occurs prior to the offgoing and oncoming clutches reaching synchronous speed (sync speed); 
 estimating, via a controller, a feed-forward clutch pressure that holds a turbine speed of the torque converter at the sync speed; 
 ramping a clutch pressure command to the oncoming clutch to the estimated feed-forward clutch pressure; and 
 initiating closed-loop proportional-integral-derivative (PID) control over the clutch pressure command during the NSB state in response to a predetermined PID activation event. 
 
     
     
       2. The method of  claim 1 , further comprising:
 exiting the NSB state only when the sync speed has been maintained for a calibrated time. 
 
     
     
       3. The method of  claim 1 , further comprising:
 exiting the NSB state when the oncoming clutch pressure has not reached the calculated feed-forward pressure within a calibrated duration. 
 
     
     
       4. The method of  claim 1 , wherein the PID activation event includes a determination, by the controller, that an actual shift time exceeds a desired shift time. 
     
     
       5. The method of  claim 1 , wherein the PID activation event includes a determination by the controller that an elapsed time since the onset of the NSB state exceeds a threshold. 
     
     
       6. The method of  claim 1 , further comprising:
 exiting PID control when the clutch speeds are synchronized for a calibrated duration. 
 
     
     
       7. The method of  claim 1 , further comprising:
 comparing the turbine speed to a calibrated upper and lower threshold; and 
 temporarily freezing a pressure command to an oncoming clutch during the clutch-to-clutch shift when turbine speed falls outside of a range defined by the upper and lower thresholds. 
 
     
     
       8. The method of  claim 1 , further comprising:
 measuring the temperature of a fluid used for actuating the clutches; and 
 using the controller to adjust the proportional, integral, and derivative gains of the PID control logic as a function of the measured temperature. 
 
     
     
       9. The method of  claim 8 , wherein the adjustment of the gains occurs in real-time during execution of the downshift. 
     
     
       10. A vehicle comprising:
 an internal combustion engine having a drive shaft; 
 a transmission having an input shaft; 
 a torque converter having a pump and a turbine, wherein the pump is connected to the drive shaft and the turbine is connected to the input shaft; and 
 a controller having a processor and tangible, non-transitory memory on which is recorded instructions for executing a method for controlling the torque phase of a clutch-to-clutch power downshift in the vehicle; 
 wherein execution of the instructions by the processor causes the controller to:
 determine, during a near sync boost (NSB) state of the power downshift, a synchronization speed of an offgoing clutch and an oncoming clutch of the transmission, wherein the NSB state is a portion of the torque phase that occurs prior to the offgoing and oncoming clutches reaching synchronous speed (sync speed); 
 estimate, via a controller, a feed-forward clutch pressure that holds a turbine speed of the torque converter at the sync speed; 
 ramp a clutch pressure command to the oncoming clutch to the estimated feed-forward clutch pressure; and 
 initiate closed-loop proportional-integral-derivative (PID) control over the clutch pressure command during the NSB state in response to a predetermined PID activation event. 
 
 
     
     
       11. The vehicle of  claim 10 , wherein the controller is configured to exit the NSB state when the sync speed has been maintained for a calibrated time. 
     
     
       12. The vehicle of  claim 10 , wherein the controller is configured to exit the NSB state when the oncoming clutch pressure has not reached the calculated feed-forward pressure within a calibrated duration. 
     
     
       13. The vehicle of  claim 10 , wherein the controller is configured to determine, as the PID activation event, that an actual shift time exceeds a desired shift time. 
     
     
       14. The vehicle of  claim 10 , wherein the controller is configured to determine, as the PID activation event, that an elapsed time since the onset of the NSB state exceeds a threshold. 
     
     
       15. The vehicle of  claim 10 , wherein the controller exits PID control when the clutch speeds are synchronized for a calibrated duration. 
     
     
       16. The vehicle of  claim 10 , wherein the controller is configured to:
 compare the turbine speed to a calibrated upper and lower threshold; and 
 temporarily freeze a pressure command to an oncoming clutch during the clutch-to-clutch shift when turbine speed falls outside of a range defined by the upper and lower thresholds. 
 
     
     
       17. The vehicle of  claim 10 , further comprising a temperature sensor positioned in a fluid used for actuating the clutches used in the downshift event, wherein the controller is configured to:
 receive the measured temperature of the fluid from the sensor; and 
 adjust the proportional, integral, and derivative gains of the PID control logic during the downshift as a function of the received measured temperature. 
 
     
     
       18. A system for a vehicle, comprising:
 a transmission having a first and a second clutch, and also having an input shaft that is connectable to a drive shaft of an engine; and 
 a controller having a processor and a tangible, non-transitory memory device on which is recorded instructions for executing a method for controlling the torque phase of a clutch-to-clutch power downshift in the vehicle, wherein the first clutch acts as an offgoing clutch and the second clutch acts as an oncoming clutch during the power downshift; 
 wherein execution of the instructions by the processor causes the controller to:
 determine, during a near sync boost (NSB) state of the power downshift, a synchronization speed of the offgoing and oncoming clutch of the transmission, wherein the NSB state is a portion of the torque phase that occurs prior to the offgoing and oncoming clutches reaching a synchronous speed; 
 estimate, via a controller, a feed-forward clutch pressure that holds a turbine speed of the torque converter at the synchronous speed; 
 ramp a clutch pressure command to the oncoming clutch to the estimated feed-forward clutch pressure; and 
 initiate closed-loop proportional-integral-derivative (PID) control over the clutch pressure command during the NSB state in response to a predetermined PID activation event. 
 
 
     
     
       19. The system of  claim 18 , wherein further comprising a temperature sensor in communication with the controller, and wherein the controller is configured to:
 receive, from the temperature sensor, a measured temperature of a fluid used for actuating the clutches; and 
 adjust the proportional, integral, and derivative gains of the PID control logic in real-time during the downshift as a function of the received measured temperature.